All types of pipes, such as water pipes, gas pipes, sewer pipes, industrial fuel, and chemical manufacturing plant pipes are susceptible to build-up of material on the inner surface of the pipe. The build-up may be a result of corrosion of the pipe surface, rust, or deposits from the material flowing through the pipe onto the pipe surface, such as lime. Such build-up leads to a narrowing of the pipe diameter, reduction of the throughput, and the formation of pits, which ultimately jeopardizes the pipe integrity and leads to premature failure of the pipe system.
Unfortunately, the replacement of pipes is not necessarily a suitable solution to such problems. One possible alternative is renovating the existing pipes, which reduces the need for a complete or partial replacement of a piping system. The interior of the pipe may be coated with an adhesive resin, such as an epoxy resin, to remedy such problems. An epoxy resin is typically made by reacting a dihydric phenol, such as bisphenol A, with excess epichlorohydrin in the presence of an alkali metal hydroxide, such as sodium hydroxide.

Typically, the resulting resin predominantly contains the diglycidyl ether of the dihydric phenol, with minor quantities of oligomer and or resin that is terminated by α-glycol groups. The dihydric phenol and the diglycidyl ether may be represented by Formula 1:
where Ar represents an aromatic group. When Formula 1 represents the dihydric phenol, each Q is a hydroxyl group. When Formula 1 represents a digycidyl ether, Q is a gylcidyl ether moiety represented by Formula (2):
Each R represents a hydrogen atom, a halogen or a lower alkyl group. “n” represents a number of repeating units. “n” may be up to about 25 in liquid epoxy resin. Typically, a small percentage of the glycidyl ether moieties (2) are hydrolyzed during this process to make α-glycol groups, which are generally represented by formula (3).

Both mono-α-glycol containing resin (in which one Q is a glycidyl ether moiety of Formula (2) and the other Q is an α-glycol of Formula (3)) and bis-α-glycol containing resin (in which both Q are α-glycol moieties of Formula (3)) may be formed. Therefore, hydroxyl groups in epoxy resins are present from many sources, including the backbone of bisphenol A diglycidyl ether (“BADGE”), mono-α-glycols, and bis-α-glycol. Such hydroxyl groups are frequently cited as accelerators for curing resins.
Usually, the mono-α-glycol resin is not detected upon curing, as it reacts during the curing process. However, bis-α-glycol is an undesirable impurity present after curing. Bis-α-glycol can be detected by analysis of water extracts from epoxy can coatings and epoxy coatings for potable water pipes and tanks. Bis-α-glycol is not normally detected in cold water extraction tests but is detected when extraction is done with water at about 82° C. (180° F.) and higher, which is commonly referred to in the plumbing and water industry as “commercial hot water.”